Contactor
A contactor is an electrically controlled switch used to repeatedly make and break power circuits, most commonly for motors, heaters, lighting and capacitor banks. A control voltage energises an electromagnetic coil that closes the main contacts; when the coil is de-energised, springs open the contacts. Auxiliary contacts provide interlocking and status signalling. Combined with an overload relay, a contactor forms a direct-on-line (DOL) motor starter. Selection is based on utilisation category (for example AC-3 for starting and switching off squirrel-cage motors and AC-1 for resistive loads), rated operational current and voltage, coil voltage (AC or DC), number of poles, mechanical and electrical endurance, and short-circuit coordination with upstream protection (Type 1 or Type 2). Low-voltage contactors are covered by IEC 60947-4-1.
Examples
- Direct-on-line starter for a small pump motor
- Contactor set in a star-delta starter
- Capacitor-switching contactor in a power factor correction panel